Although I'm quite familiar with Mathematica, I always try to keep an open mind and don't use it as golden hammer.
Officially, I'm working in image and data processing, but in my free-time, I'm particularly good at things that are fun, for instance

glueing QR codes on paper roles and writing articles about it

implementing a Mathematica plugin for the best IDE ever just because I was curious whether I can hack a complete Mathematica parser

making images that give you a headache

making stackexchange better by hacking a highlighter for Mathematica code-blocks in Java Script or abusing others hard work to extend our own markup editor on mathematica.se